140psi is definitely no problem for our 23-622 Ultremo DD. Our 25-622 Ultremo DD is limited to 130psi, but shouldn´t blast up to 290psi anyway!I guess tire and rim size suit each other, right (both 622)?The tube is not clamped in between rim horn and tire bead?Can you see any defect at the bead area?

I suppose someone includes me. Overtensioning can crack nipple holes, crack or deform nipple heads, bring the spoke thread closer to the tube, distort the rim. The higher the tube pressure, the more the tube will push into/against the nipple head or protruding spoke thread. A tube that bursts under high pressure can blow a rim off.

Putting cost aside, I think it would be very interesting to see whether Comedian's problem persisted after a wheel rebuild on the C50s. It would also be a meaningful troubleshooting step to put Comedian's blowing tires on several of his mate's wheels. If they don't blow off those, what's to be made of that?

The RS80-C50 are a deep section wheel, I don't think that the spoke thread is going to protrude out of the hole. If the spokes were to protrude out of their holes (on say something shallower) it means your spokes are too long. If the high tension does indeed distort the rim, the wheel would not be true and I'm sure the OP would have noticed that... Or am I missing something?

140psi is definitely no problem for our 23-622 Ultremo DD. Our 25-622 Ultremo DD is limited to 130psi, but shouldn´t blast up to 290psi anyway!

I'm going to call BS on their claim that the tyre should stay on the rim up to 290psi. I don't know of any clincher rim that'll even handle that kind of pressure.

The process you're following if anything is far too careful, I've never done ANY of that stuff and have never had a road tyre blow off.

I'm feeling that you're stretching the casing when you are going to those 130-140psi pressures, at this point in time my money is that this is the cause of your problem and the tyres that you've done that with are toast. You shouldn't ever have a requirement to pump a clincher past 120psi and unless you are a really heavy rider 120psi is too much for most people.

Easy enough to test.

Get yet another new set - don't pump them past 110-115psi and see how you go.

If you want to really take care of your tyres and take it a step further, let them down to 60-80psi inbetween rides. I do this on my race clinchers and the tyres are always TIGHT on the rims even after sometime. Whereas my training tyres that are left pumped up are quite loose on the rim by the end of their life.

The rim tape may have stretched due to age, regular high PSI, heat exposure within a car boot....and may not be protecting tubes from sharp rim holes and high PSI....in which case a layer or two of new tape (reinforced at valve hole), or veloplugs would be informative.

From what I understand the problem hasn't always existed with these tires for Comedian. So either something about the tires has changed, or the wheels, or both.

I know that technique issues have been raised and brushed off before so I am only restricting my comment to the most recent failure and the fact that it coincided with the valve. Since the tube has a patch of reinforcing there it is a common place to pinch a tube. I also note that Comedian's valves only barely make it out of the deep rims.

FWIW I always install a tyre and finish at the valve since the finish point is the most likely for a tube pinch. The reason that I finish at the valve is so that I can push the valve back though the rim into the tyre as far as it will go. This is enough to be absolutely sure that there is no pinch at that point.

As for excessive pressure that is not the problem. Tandem riders routinely exceed the recommended pressures and experience no problems with cold tyres. (Heating tyres up with rim brake use does cause problems though and this is well known, but pressure alone is not an issue)

stnfldr wrote:I had the same problem once, turns out I hadnt taken the little valve nut of the valve, so every time i inflated the tyre it popped off the rim......

this is an easy mistake to make - i've done it numerous times. where the valve is molded into the tube, the tube is more rigid. it is easy for that section of tube to become wedged under the tyre bead and as you inflate it, lift the bead off the rim.

the trick is to ensure the tube, where the valve is molded into it, is stuffed high up into the tyre. it's important to remember that pulling the valve downwards to allow the pump chuck to gain a good purchase on the valve may interfere with that, by pulling the tube down below the tyre bead. a solution here is long valves.

i would imagine such a failure would be more likely to occur along the section of rim at which the spokes attach (i.e. the inner section, not the outer tyre seat as shown). either way, would that crack cause the tyre to blow off the rim?

jules21 wrote:i would imagine such a failure would be more likely to occur along the section of rim at which the spokes attach (i.e. the inner section, not the outer tyre seat as shown). either way, would that crack cause the tyre to blow off the rim?

a crack isn't excluded from where there's an extrusion weakness.if a tube is pumped to high enough pressure, it could open the crack further, and move into it, burst, and blow the tire.

winstonw wrote:the crack will occur where the extrusion weakness is. if a tube is pumped to high enough pressure, it could open the crack further, and move into it, burst, and blow the tire.

fair enough. but "blow the tire (up)" and "blow the tire off the rim" are different, as i interpret them. what we're discussing is the tire bead unhooking from the rim seat, not the tyre itself failing.

I've seen tires blow off the rim before, on bikes not moving, and it was always accompanied by a blown tube. Whether the tube blew first, or the tire moved enough to come off then cause the tube to blow, was impossible to tell.

winstonw wrote:I've seen tires blow off the rim before, on bikes not moving, and it was always accompanied by a blown tube. Whether the tube blew first, or the tire moved enough to come off then cause the tube to blow, was impossible to tell.

yep - which was my original question. the suggestion was spoke tension could cause it. we're no closer to knowing how

jacks1071 wrote:That looks more like a fatigue crack caused possibly by excessive tyre pressure. Exactly why you shouldn't run too much pressure in a clincher.

Spoke tension isn't going to crack the rim in that spot, the nipples anchor in the outer edge.

That might be more appropriate for a perfect wheel. But as my wheel builder alluded, rim extrusion faults or real world rims possibly compromised by heavy pothole hits or bunny hops requires a subtler approach to troubleshooting. Barnett's Manual also says: "Cracks around nipple holes or at the inner perimeter of the sidewall usually indicate excessive spoke tension."

jules21 wrote:i suspect jacks meant the "inner edge" - which is where the spokes anchor and where your manual suggests they'd crack.

Yes exactly. That being said, cracks around the nipples can be just as easily caused by not enough tension as they can by excessive tension. Not to mention good old fashioned wear and tear - metals fatigue and everything has a useable life. Premature failures though, either too little, or too much spoke tension.

If you get a split up the middle of the rim where the tube sits (ie. under the rim tape) - this most likely excessive pressure related in my opinion. Its not uncommon for full carbon clinchers to have similar failures. Less common, I'd even say very rare on alloy wheels. As you increase the pressure, the tyre bead is trying to open the rim up like a banana.

winstonw wrote:Jack (deon?), do you think a wheel tensioned to 50kgf will be harder/easier to fit a tire to than the same wheel tensioned to 200kgf?

Why would you try to fit a tyre to a pringle?

I presume that you are trying to suggest that at higher tension the BSD of the rim is less than at lower tension. This may have been true of the old pinned rims with a visible gap at the join that closed under tension (Fiamme Red label anyone?), but if there is a difference in a welded or bonded rim it is negligible. How much do you reckon that you can compress aluminium? (or CFRP)

I have seen a theme in your posts that you seem to believe that an exploding tube can blow a tyre off a rim. I do not believe this. The bang occurs when the tube suddenly expands such as when it is no longer contained, either when the bead lifts off the rim, or there is a failure of the sidewall. Internal punctures off spokes, cracks etc tend to cause a rapid pssst but not a bang IME. Uncontained tubes will explode at very low pressure differentials, 10psi or so, tubes that are contained within a pressure vessel such as a rim, tape, tyre combination do not have to support any pressure differential because the container is providing the support. If that support is taken away such as when the bead lifts off the rim the tube will go bang.

BTW spoke tension will not cause the cracking on the tube side of a rim. Spoke tension will in fact act to draw the sidewalls of the rim together (weakly), whereas air pressure is trying to tear the sidewalls apart and is a much more likely cause.

winstonw wrote:Jack (deon?), do you think a wheel tensioned to 50kgf will be harder/easier to fit a tire to than the same wheel tensioned to 200kgf?

I don't think it'd make any difference. The spokes are to support the rim, I don't think cranking the tension is going to reduce the overall diameter of the wheel.

I've fitted tyres to rims that wern't built up for displays and they were no easier or harder than a fully assembled wheel.

The more I think about this issue, the more I am confident that the OP is stretching the tyres by over inflating them. Although he's well within what the tyre manufacturer says the tyre is capable of I don't think the tyre manufacturer's "max" is realistic.

This is assuming his rims arn't all cracked up the centre like one of the pictures someone posted

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